Statements Of Unaudited Condensed Consolidated Operations - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
REVENUES FROM PRODUCT SALES AND SERVICES
Product	$ 672.0	$ 417.0	$ 841.2	$ 664.3
Freight and venture partners' cost reimbursements	42.3	54.3	53.1	93.2
TOTAL REVENUES	714.3	471.3	894.3	757.5
COST OF GOODS SOLD AND OPERATING EXPENSES	(429.8)	(326.6)	(548.3)	(563.8)
SALES MARGIN	284.5	144.7	346.0	193.7
OTHER OPERATING INCOME (EXPENSE)
Selling, general and administrative expenses	(26.2)	(26.6)	(51.3)	(51.7)
Miscellaneous - net	(4.1)	(2.9)	(10.2)	6.6
Other operating expense	(30.3)	(29.5)	(61.5)	(45.1)
OPERATING INCOME	254.2	115.2	284.5	148.6
OTHER INCOME (EXPENSE)
Interest expense, net	(31.2)	(30.1)	(63.6)	(71.5)
Gain (loss) on extinguishment of debt	0.2	(4.9)	0.2	(76.8)
Other non-operating income	4.4	2.5	8.8	5.0
TOTAL OTHER INCOME (EXPENSE)	(26.6)	(32.5)	(54.6)	(143.3)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	227.6	82.7	229.9	5.3
INCOME TAX BENEFIT (EXPENSE)	1.8	1.1	(13.9)	0.0
INCOME FROM CONTINUING OPERATIONS	229.4	83.8	216.0	5.3
LOSS FROM DISCONTINUED OPERATIONS, NET OF TAX	(64.3)	(53.7)	(135.2)	(5.0)
NET INCOME	165.1	30.1	80.8	0.3
LOSS ATTRIBUTABLE TO NONCONTROLLING INTEREST	0.0	1.7	0.0	3.4
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS	$ 165.1	$ 31.8	$ 80.8	$ 3.7
INCOME (LOSS) PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS – BASIC
Continuing operations (in dollars per share)	$ 0.77	$ 0.28	$ 0.73	$ 0.03
Discontinued operations (in dollars per share)	(0.22)	(0.18)	(0.46)	(0.01)
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Basic (in dollars per share)	0.55	0.10	0.27	0.02
INCOME (LOSS) PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS – DILUTED
Continuing operations (in dollars per share)	0.76	0.28	0.72	0.03
Discontinued operations (in dollars per share)	(0.21)	(0.18)	(0.45)	(0.02)
Earnings (Loss) per Common Share Attributable to Cliffs Common Shareholders - Diluted (in dollars per share)	$ 0.55	$ 0.10	$ 0.27	$ 0.01
AVERAGE NUMBER OF SHARES (IN THOUSANDS)
Basic	297,618	296,100	297,442	280,617
Diluted	301,275	300,700	301,143	285,247